Dipyridamole for preventing stroke and other vascular events in patients with vascular disease

Patients with transient ischaemic attacks (TIA) and minor ischaemic strokes are at risk of serious vascular events (death from all vascular causes, non-fatal stroke, or non-fatal myocardial infarction). Their risk of vascular events lies between 4 and 11 percent per year. Aspirin only, in a daily dose of 30 mg or more, offers only modest protection in such patients: it reduces the incidence of major vascular events by 13 percent. In a single trial, adding dipyridamole (an alternative antiplatelet agent) to aspirin was associated with a 22 percent reduction in the risk of major vascular events compared with aspirin alone. However, a systematic review of all trials of antiplatelet agents by the Antithrombotic Trialists' Collaboration showed that, in high risk patients, there was virtually no difference between the aspirin-dipyridamole combination and aspirin alone. We therefore sought to assess the effects of dipyridamole in more detail.

1) To assess the efficacy of dipyridamole versus control in the secondary prevention of vascular events in patients with vascular disease in the presence and absence of other antiplatelet drugs. 2) To assess the safety of dipyridamole versus control in the secondary prevention of vascular events in patients with vascular disease in the presence and absence of other antiplatelet drugs.

The Cochrane Stroke Group Trials Register was searched and other relevant Cochrane Groups were contacted to search their specialised registers (last search 29 April 2002). In addition the Cochrane Controlled Trials Register, MEDLINE and EMBASE were searched and Dutch manufacturers of dipyridamole were contacted to identify further published and unpublished studies.

Randomised long term secondary prevention trials with concealed treatment allocation, treatment for > 1 month, starting within 6 months after presentation of a arterial vascular disease were selected (coronary artery disease, myocardial infarction, angina pectoris, retinopathy, nephropathy, peripheral arterial disease, stroke, TIA, amaurosis fugax). Therapy consisted of dipyridamole in any dose in the presence or absence of other antiplatelet drugs compared with no drug or an antiplatelet drug(s) other than dipyridamole (control group).

Two reviewers selected trials which met the inclusion criteria and extracted details of randomisation methods, blinding of treatments and assessments, whether intention-to-treat analysis was possible from the published data, whether treatment groups were comparable with regard to major prognostic factors, the number of patients who were excluded or lost to follow-up, definition of outcome events, and entry and exclusion criteria. The methodological quality of each trial was assessed by the two reviewers on the basis of these extracted data. In addition, dose and type of antiplatelet treatments, duration of follow-up and the numbers of defined outcome events were recorded. Data published by the Antithrombotic Trialists' Collaboration were used. The remaining data were independently extracted by the same two reviewers and cross checked. Data were analysed according to the intention-to-treat principle. Relative and absolute risk reductions were calculated by means of the statistical software provided by the Cochrane Collaboration (RevMan).

Twenty-six trials were included, with a total of 19842 patients, among whom 1399 vascular deaths and 3085 fatal and non-fatal vascular events occurred during follow-up. Compared with control, dipyridamole had no clear effect on vascular death (RR 1.02, 95% CI 0.90 to 1.17). This result was not influenced by the dose of dipyridamole or type of presenting vascular disease. Compared with control, dipyridamole appeared to reduce the risk of vascular events (RR 0.90, 95% CI 0.83 to 0.98), but this effect was only statistically significant due to a single large trial in patients presenting with cerebral ischaemia (6602 patients). Comparing dipyridamole plus aspirin with aspirin alone: there was no clear difference in vascular death, the RR was 1.03 (95% CI 0.87 to 1.22); the combination was associated with fewer vascular events with an RR of 0.90 (95% CI 0.80 to 1.00). Combination treatment of dipyridamole and aspirin compared with placebo had an RR of 0.89 (95% CI 0.79 to 1.01) for vascular death and an RR of 0.74 (95% CI 0.68 to 0.80) for vascular events.

This review found that, for patients who presented with arterial vascular disease, there was no evidence that dipyridamole, in the presence or absence of an other antiplatelet drug (chiefly aspirin) reduced the risk of vascular death, though it may reduce the risk of further vascular events. However, this benefit was found in only a single large trial and only in patients presenting after cerebral ischaemia. There was no evidence that dipyridamole alone was more efficacious than aspirin. Further trials comparing the effects of the combination of dipyridamole with aspirin with aspirin alone are justified.